The invention relates to transparent substrates, in particular made of a rigid inorganic material such as glass, the said substrates being coated with a stack of thin layers comprising at least one layer having a metallic-type behaviour able to act on solar radiation and/or long-wavelength infrared radiation.
The invention relates more particularly to the use of such substrates to manufacture thermal-insulation and/or solar-protection glazing assemblies. These glazing assemblies are intended to equip both buildings and vehicles, with a view in particular to decreasing the air-conditioning load and/or to reducing excessive overheating caused by the ever growing extent of glazed surfaces in passenger compartments.
A known type of multilayer stack for giving the substrates such properties consists of at least one metallic layer, such as a silver layer, which is placed between two coatings of dielectric material of the metal-oxide type. This stack is generally obtained by a succession of depositions carried out using a vacuum technique, such as sputtering, optionally assisted by a magnetic field. Two very thin metal layers may also be provided on either side of the silver layer, the subjacent layer acting as a tie layer for nucleation and the overlayer as a protective or xe2x80x9csacrificialxe2x80x9d layer so as to prevent degradation of the silver if the oxide layer which is on top of it is deposited by sputtering in the presence of oxygen.
Stacks of this type, having one or two base layers of silver, are thus known from European Patents EP-0,611,213, EP-0,678,484 and EP-0,638,528.
Currently, there is an increasing demand for these low-emissivity or solar-protection glazing assemblies which have in addition characteristics inherent in the substrates themselves, in particular aesthetic characteristics (so that they can be shaped), mechanical properties (so that they are stronger) or safety characteristics (so that they do not cause injury in the event of breakage). This requires the glass substrates to be subjected to heat treatments known per se, of the bending, annealing and toughening type. Laminated-type glazing assemblies intended to be fitted into vehicles, which are nowadays almost all curved and/or toughened, are particularly intended.
It is therefore necessary to adapt the multilayer stack in order to preserve the integrity of the functional layers of the silver-layer type, in particular to prevent their degradation. A first solution consists in significantly increasing the thickness of the thin metal layers, mentioned above, which surround the functional layers: in this way it is ensured that any oxygen likely to diffuse from the ambient atmosphere and/or migrate from the glass substrate at high temperature be xe2x80x9ccapturedxe2x80x9d by these metal layers, by oxidizing them, without it reaching the functional layer(s).
This solution is not without drawbacks: since the two metal layers readily oxidize xe2x80x9cinstead ofxe2x80x9d the silver layers, they lead in particular to a great increase in the light transmission TL; it is thus possible to obtain a low-emissivity or solar-protection glazing assembly, which is curved or toughened, having a value of TL greater than 75 and up to 80%, though this value was much lower before the heat treatment. In particular, reference may be made to Patent Application EP-A-0,506,507 for the description of such a xe2x80x9ctoughenablexe2x80x9d stack with a silver layer placed between a tin layer and a nickel-chrome layer. However, it is clear that the coated substrate before heat treatment was regarded only as a xe2x80x9csemi-finishedxe2x80x9d product and the optical properties frequently made it unusable as such. It was therefore necessary to develop and manufacture, in parallel, two types of multilayer stack, one for the non-curved/non-toughened glazing assemblies and the other for glazing assemblies intended to be toughened or curved, which may complicate matters, in particular in terms of stock and production control.
An improvement proposed in Patent EP-0,716,250 has made it possible to overcome this constraint: the teaching of this document consists in designing a stack of thin layers such that its optical and thermal properties remained virtually unchanged, whether or not the substrate, once coated with the stack, underwent a heat treatment. Such a result is achieved by combining two characteristics;
on the one hand, provided on top of the functional layer(s) is a layer made of a material capable of forming a barrier to oxygen diffusion at high temperature, which material itself does not undergo chemical or structural modification at high temperature which would result in modification in its optical properties. This material may thus be silicon nitride Si3N4 or aluminium nitride AlN;
on the other hand, the functional layer(s) is (are) directly in contact with the subjacent dielectric coating, in particular zinc oxide ZnO.
Although this solution allows the substrate effectively to maintain a TL level and an appearance in external reflection which, after heat treatment, are quite constant, it is still capable of improvement, in that it has been observed with this type of stack that optical defects, sometimes visible to the naked eye, could appear after heat treatment, these very often being in the form of a speckling of bright spots of the xe2x80x9cpinholexe2x80x9d type or having a slightly fuzzy appearance, which is obviously prejudicial in terms of the aesthetic appearance and of productivity since this may lead to an abnormally high scrap rate, most particularly if these glazing assemblies are curved/toughened glazing assemblies, which may or may not be of the laminated types intended for fitting into vehicles of the motor-vehicle type, in which very strict standards impose a very high optical quality.
The object of the invention is therefore to succeed in remedying this drawback, in particular by developing a novel type of stack having a functional layer or layers, of the type of those described previously, which stack is able to undergo high-temperature heat treatments of the bending/toughening or annealing type, while preserving its optical quality.
The subject of the invention is a glazing assembly comprising at least one transparent substrate provided with a stack of thin layers which includes an alternation of n functional layer(s) having reflection properties in the infrared and/or in solar radiation, in particular of an essentially metallic nature, and of (n+1) xe2x80x9ccoatingsxe2x80x9d, with nxe2x89xa71. The said xe2x80x9ccoatingsxe2x80x9d are composed of a layer or a plurality of layers, at least one of which is made of a dielectric material. These functional layers and these coatings are arranged so that the (each) functional layer is placed between two coatings.
With a view to preserving the optical quality of the stack in the case where the substrate once provided with the stack is subjected to a heat treatment of the toughening, bending, annealing type:
on the one hand, the coating placed on top of the functional layer, or on top of one of the functional layers, and in the latter case preferably the nth layer, includes at least one xe2x80x9cbarrierxe2x80x9d layer made of a material capable of forming a barrier at least to oxygen and water; and
on the other hand, at least one xe2x80x9cabsorbentxe2x80x9d or xe2x80x9cstabilizingxe2x80x9d layer made of a material capable of xe2x80x9cabsorbingxe2x80x9d or xe2x80x9cstabilizingxe2x80x9d the constituent material of the said functional layer forms part of:
either the coating placed on top of the said functional layer and under the xe2x80x9cbarrierxe2x80x9d layer;
or the coating placed under the said functional layer.
Preferably, the barrier layer is made of a material capable of also forming a barrier to the constituent material of the functional layer.
The inventors have in fact demonstrated that the appearance of optical defects after heat treatment of this type of stack of thin layers arose essentially from the migration of part, even a very small part, of the constituent material of the functional layer into the layers which are adjacent to it. The term xe2x80x9cconstituent materialxe2x80x9d is understood to mean, when the layer is metallic, both the metal element in question and the possibly totally or partially ionized metal. Thus, when the functional layer is wade of silver, the migration of silver both in the form of Ag and Ag+ into the upper layers, i.e. those placed on top of it, was observed, this migration resulting in the formation of silver xe2x80x9cclustersxe2x80x9d on the surface of the stack, creating an unattractive speckling.
Two reasons for this migration have been proposedxe2x80x94on the one hand, a mechanical reason and, on the other hand, a chemical reason.
From the mechanical standpoint, when the stack is heated to high temperature, in particular within the temperature range of from 550 to 650xc2x0 C. which is necessary for the usual operations of bending and/or toughening the glazing assemblies, all the materials making up the thin layers xe2x80x9creact differentlyxe2x80x9d to this thermal stress. The functional layer made of metal of the silver type will expand greatly and, in general, more than the other layers of the stack, in particular those based on a dielectric which are contiguous with it. The functional layer will therefore be in a high state of compression at high temperature, and the silver, in metallic and/or ionic form, then tends to embrittle, with a decrease in the adhesion of the layer to the contiguous layers, until it has a tendency to migrate into the other layers in order to relieve the thermomechanical stress to which it is subjected.
From the chemical standpoint, if this time the adjacent layers, and more particularly the layers placed on top of it, are not capable of completely blocking this migration, the optical defects mentioned above then appear. This may be the case when there are, as dielectric coatings placed on top of the functional layer, known materials of the metal-oxide type, or even materials chosen for forming an oxygen barrier so as to prevent the migration of oxygen from the outside into the functional layer, as is the case with Si3N4.
The invention therefore consisted in providing a double protection for the functional layer of the silver type.
It was important to continue to provide on top of the functional layer at least one layer made of a material capable of preventing the migration of oxygen and water from the ambient atmosphere into the functional layer, this diffusion rising from the atmosphere proving to be of greater magnitude and markedly more prejudicial to the integrity of the functional layer than the possible migration of oxygen which stemmed this time from the glass. (However, provision may also be made, for maximum safety, also to place this type of xe2x80x9cbarrierxe2x80x9d layer under the functional layer). This thus avoids any chemical modification of the functional layer, in particular by oxidation/hydration, which would decrease its thermal performance characteristics and would call into question its optical quality, this chemical degradation phenomenon being uncontrollable.
However, the invention adds to this first protection, according to a first variant, a means for capturing, and absorbing the silver which would tend to migrate out of the layer, this being achieved with the aid of a layer capable of receiving a certain amount of constituent material of the functional layer which is xe2x80x9cin excessxe2x80x9d under the thermomechanical stress. This so-called xe2x80x9cabsorbentxe2x80x9d layer thus makes it possible to stop the migration into the other layers of the stack as far as the external atmosphere.
Its place in the stack can be varied. If it is placed on top of the functional layer, it is preferable, in order for it to be able to fulfil its role, for it to be under the barrier layer mentioned previously in order to prevent there being any migration through the barrier layer, creating the optical defects mentioned previously, i.e. the formation of xe2x80x9cclustersxe2x80x9d of material coming from the functional layer, in particular silver, which are responsible for the unattractive speckling. However, provision may also be made for it to be placed under the functional layer.
In fact, the xe2x80x9cabsorbentxe2x80x9d layer is to be chosen so that it preferably has at least two properties: it is important, on the one hand, that the material of which it is composed has a good chemical affinity with the material of the functional layer and, on the other hand, that the material of the absorbent layer is able to capture the xe2x80x9cexcessxe2x80x9d material of the functional layer, it being possible for the method of incorporating this xe2x80x9cexcessxe2x80x9d material to be carried out in various ways, in particular by incorporation of the interstitial type or of the vacancy type.
According to a second variant, it is preferred to use not an xe2x80x9cabsorbentxe2x80x9d layer but rather a xe2x80x9cstabilizingxe2x80x9d layer. In the sense of the invention, xe2x80x9cstabilizingxe2x80x9d means that the nature of the layer in question is selected so as to stabilize the interface between the functional layer and this layer. This stabilization leads to an increase in the adhesion of the functional layer to the layers which surround it, and thus resists the migration of its constituent material generally in a direction taking it away from the carrier substrate.
It has turned out that one particularly advantageous material for forming this xe2x80x9cstabilizingxe2x80x9d layer is zinc oxide, preferably placed on top of the functional layer in order to resist in an optimum manner the diffusion from the opposite side of the stack from the class substrate, either directly or via a thin metal layer of the sacrificial type (the thickness is generally about 0.5 to 2 nm). (It may also be under the functional layer, preferably directly in contact with it). This ZnO-based xe2x80x9cstabilizingxe2x80x9d layer advantageously has a thickness of at least 5 nm, in particular between 5 and 25 nm.
The invention applies not only to stacks having only a single xe2x80x9cfunctionalxe2x80x9d layer placed between two coatings. It also applies to stacks which include a plurality of functional layers, in particular two functional layers alternating with three coatings, of the type described, for example, in Patent EP-0,638,528, or three functional layers alternating with four coatings, of the type described, for example, in Patent EP-0,645,352.
If the stack thus uses several functional layers, it has proved to be the case that it was often advantageous for the last functional layer, the one furthest away from the carrier substrate, of the stack to be provided both with a barrier layer and with an absorbent or stabilizing layer, as it seems that it was the latter which was most xe2x80x9cexposedxe2x80x9d because of its position in the stack, in the sense that it was the most likely to be oxidized by the ambient atmosphere and the one from which part of its constituent material could migrate the most easily as far as the external surface of the last layer of the stack.
Of course, provision may be made for all the functional layers to be thus provided with a barrier layer and with an absorbent or stabilizing layer according to the invention, in particular made of silver or a metal alloy containing silver.
The barrier layer according to the invention is preferably chosen from dielectric materials whose refractive index is advantageously similar to those normally used in this type of sack, i.e. lying in particular between 1.7 and 2.5. It may thus xe2x80x9copticallyxe2x80x9d replace the dielectric layers of the metal-oxide type and combine an interferential optical function with a barrier function.
The barrier layer is, in particular, based on silicon compounds of the silicon oxide SiO2, silicon oxycarbide SiOxCy or silicon oxynitride SiOxNy type. It may also be based on nitrides, of the silicon nitride Si3N4 or aluminum nitride AlN type, or a mixture of at least two of these compounds.
It may also be chosen to be of the carbide type, such as SiC, TiC, LiC and TaC, but then it is preferred to limit it to thicknesses which are not too great, because of their absorbent character which may penalize the stack in terms of the level of light transmission TL if it is desired to obtain a glazing assembly with a high TL.
In general, the geometrical thickness of the barrier layer is otherwise preferably selected, so that it is at least 10 nm, in particular at least 15 nm or especially between 15 and 60 nm or more especially between 20 and 50 nm.
Let us now turn our attention to the arrangement in the stack and to the nature of the absorbent layer according to the first variant of the invention. It has been seen that it must enable the state of compression of the functional layer at high temperature to be reduced by allowing part of its material, particular in metallic or ionic form, to be incorporated. It may be placed either directly in contact with the functional layer, under it or on top of it, or it is separated from it by at least one xe2x80x9cinterlayerxe2x80x9d which is xe2x80x9cpermeablexe2x80x9d to the migration of the material in metallic or ionic form at high temperature, without this resulting in a chemical or structural modification of the said interlayer having a prejudicial impact on the optical appearance of the stack in its entirety. This interlayer or these interlayers, able to be between the functional layer and the absorbent layer are in particular the thin metal layers which serve as nucleation layers or as sacrificial layers with respect to the functional layer.
According to a first embodiment, the material of the absorbent layer is chosen from a porous material, in particular a layer having a porosity of at least 2% and preferably between 5 and 25%. Porosity is defined here by the relationship p %=1xe2x88x92(d1/d0), where d0 is the theoretical density of the material in question as a percentage and d1 its actual density. This porosity is often manifested, when the material is a dielectric, by a reduction in its refractive index compared to its theoretical index, approximately in the same proportions as its density. In order to provide a sufficient absorption capacity, provision is generally made for this porous layer to have a geometrical thickness of at least 2 nm, in particular between 2 and 30 nm; it is possible to vary both the porosity and the thickness in order to obtain the desired effect of complete absorption of the material of the functional layer which is xe2x80x9cin excessxe2x80x9d.
According to a first case, this porous layer may be essentially metallic, in particular made of a material chosen from at least one of the following metals: Ni, Cr, Nb, Sn, Ti, an alloy of the NiCr type or steel. In this case, it is preferable to limit its thickness to a range of from 2 to 5 nm, as its optically absorbent nature would, if a thicker layer were to be chosen, decrease the level of light transmission too significantly when it is desired to have a highly transparent glazing assembly.
According to a second case, the porous layer is chosen from a dielectric material, in particular a material chosen from at least one of the following oxides: zinc oxide ZnO, titanium oxide TiO2, silicon oxide SiO2 and aluminium oxide Al2O3. In this case, the layer may be appreciably thicker and also fulfil its interferential role in the stack.
The porosity of these various materials may be varied by adjusting the deposition conditions. Thus, when these layers are deposited by sputtering, optionally assisted by a magnetic field, the choice of the pressure within the deposition chamber makes it possible to control the porosity of the layer; the higher the pressure of the inert gas, of the argon type, the greater the tendency for the porosity to increase.
According to a second embodiment, the material of the absorbent layer consists of a material capable of reversibly or irreversibly inserting the ions of the metal of the functional layer, and possibly the un-ionized metal, and possibly ionizing the material at the moment of inserting it. This is in particular a material based on at least one of the following components: tungsten oxide WO3, nickel oxide NiOx, niobium oxide NbOx, iridium oxide IrOx, tin oxide SnOx, and vanadium oxide VOx, it being possible for these oxides to be substoichiometric in terms of oxygen, and either hydrated or non hydrated. In fact, these materials, in particular tungsten oxide, are well-known for their properties of reversibly inserting cations of the Ag+ type in electrochromic windows or devices.
The thickness of this type of insertion layer can be varied, in particular depending on its intrinsic insertion capacity with respect to each of the materials mentioned. Preferably a layer of at least 1 nm, in particular between 1 and 50 nm, preferably between 2 and 30 nm, is provided.
According to a third embodiment, the absorbent layer essentially consists of a metal (or of a metal alloy) capable of forming a defined or non-defined solid solution with the metal of the functional layer when it is metallic. Mention may be made in particular of at least one of the following metals or metalloids: Cu, Pd, Zn, Au, Cd, Al and Si. The term xe2x80x9csolid solution is understood to mean here an association which is not necessarily strictly speaking an alloy, but one in which the metal of the absorbent layer can xe2x80x9cdissolvexe2x80x9d a certain amount of the metal of the functional layer into its matrix, forming a compound which may be of undefined stoichiometry, i.e. a metal which can incorporate a variable amount of metal of the functional layer, an amount xe2x80x9cstartingxe2x80x9d from 0% and able to increase progressively.
Provision may also be made for the materials of the second and third embodiments to have a porosity such as that defined in the first embodiment.
Advantageously, provision may be made for at least one of the functional layers to be surmounted by a thin xe2x80x9csacrificialxe2x80x9d metallic layer which is at least partially oxidized, in particular having a thickness of from 0.5 to 4 nm: the latter makes it possible to preserve the functional layer from oxidation, during the deposition of the stack, when the next layer is based on an oxide deposited by reactive sputtering in the presence of oxygen. The xe2x80x9csacrificialxe2x80x9d layer thus oxidizes in place of the metal of the functional layer.
Provision may therefore be made for the metallic-type absorbent layer, in particular one which is porous and/or capable of forming a solid solution, to be placed directly on top of the functional layer and therefore also to act as a xe2x80x9csacrificialxe2x80x9d layer. In this case, it must be sufficiently thick so that, after it has oxidized during the deposition of the upper layer, there remains a sufficient thickness of non-oxidized metal capable of fulfilling its role as an absorber.
Advantageously, the stack comprises two functional layers, with each of which are associated a barrier layer and an absorbent or stabilizing layer.
In the stack, the barrier layer or at least one of the barrier layers may constitute the essential aspect of the coating in the sense of the invention. It may also be combined with other layers of dielectric material and may, in particular, be surmounted by at least one other layer based on a metal oxide or oxides, such as zinc oxide ZnO, tin oxide SnO2, titanium oxide TiO2, niobium oxide Nb2O5, tantalum oxide Ta2O5, aluminium oxide Al2O3 and tungsten oxide WO3, or any mixture of at least two of these oxides. There are in particular two ways of carrying out the deposition of this oxide layer: either, in the usual way, directly in the form of oxide or, in particular when it constitutes the final layer of the stack, in the metallic form, its oxidation then being carried out after its deposition, most particularly during the heat treatment in air of the substrate. Its thickness is preferably chosen to be between 0.5 and 20 nm, in particular between 1 and 5 nm, but of course it remains optional. The reasons may be many, in particular they may take into account the rate of deposition of these layers, the cost of the raw materials (the targets if a sputtering deposition technique is used) and the refractive indices. The judicious choice of the layer or layers surmounting the barrier layer may also take into account the optimization of the adhesion of the stack to the sheet of thermoplastic polymer of the polyvinyl butyral PVB type when the substrate coated with the stack is mounted with a laminated glazing assembly. (In this regard, the teaching of Patent EP-0,433,136 may thus be indicated). This choice may also take into account the chemical-corrosion and/or mechanical problems that the stack may have to overcome, for example depending on the atmosphere with which it will come into contact, either during the process for manufacturing the glazing assembly (for example, the atmosphere during the heat treatment) or while it is being stored or once it has been installed.
Moreover, provision may also be made for the functional layer, or at least one of the functional layers, to be placed on a coating, the final layer of which facilitates wetting of the functional layer. This may more particularly be a wetting layer based on zinc oxide ZnO, niobium oxide Nb2O5 or tantalum oxide Ta2O5, or a sequence of two layers of this type. For further details, reference may be made to Patents EP-0,611,213 and EP-0,678,434. It is not excluded for these wetting layers, by choosing them so as to be porous, also to be able to fulfil the role of absorbent layers or, by selecting their thickness and their configuration, that of stabilizing layers.
According to one embodiment of the invention, at least one of the functional layers is surmounted by a coating comprising the sequence absorbent or stabilizing layer/barrier layer of the SnO2/Si3N4 or WO3/Si3N4 or ZnO/Si3N4 type, it being possible for Si3N4 to be replaced, for example, by AlN or by a mixture of AlN and Si3N4.
The glazing assembly according to the invention may also be such that, in particular in the case of a stack having two silver-based functional layers, at least one of these layers, in particular the final one, is on top of a coating comprising the sequence ZnO/Si3N4/ZnO.
This glazing assembly may also be such that at least one of the functional layers, in particular the first one, is on top of a coating comprising the sequence SnO2/ZnO or Si3N4/ZnO.
According to a second embodiment, there is this time a sequence of the absorbent or stabilizing layer/functional layer/barrier layer type (possibly with xe2x80x9cinterlayersxe2x80x9d on either side of the functional layer) with, in particular, a layer of SnO2 or WO3 or ZnO under the functional layer and a layer of Si3N4 and/or AlN on top of the functional layer.
The glazing assembly according to the invention includes at least the substrate carrying the stack, possibly combined with at least one other substrate. They may all be clear, or coloured, particularly at least one of the substrates may be made of bulk-coloured glass. The choice of the type of coloration will depend on the level of light transmission and/or on the calorimetric appearance which are desired for the glazing assembly once its manufacture has been completed. Thus, for glazing assemblies intended for fitting into vehicles, standards demand that the windscreen have a light transmission TL of approximately 75%, such a level of transmission not being required for the side windows or the sun-roof, for example. The tinted glasses which may be adopted are, for example, those which, for a thickness of 4 mm, have a TL of from 65% to 95%, an energy transmission TE of from 40% to 80% and a dominant wavelength in transmission of from 470 nm to 525 nm combined with a transmission purity of from 0.4% to 6% using the D65 illuminant, which may be xe2x80x9cmanifestedxe2x80x9d in the (L, a+, b+) colorimetry system by values of a+ and b+ in transmission of, respectively, between xe2x88x929 and 0 and between xe2x88x928 and +2.
These may be the glasses sold under the name PARSOL by Saint-Gobain Vitrage, in particular those having a verdigris tint. They may also be glasses of the so-called xe2x80x9cTSAxe2x80x9d range which are also sold by Saint-Gobain Vitrage, and glasses whose composition and properties are in particular described in Patents EP-0,616,883, EP-0,644,164, EP-0,722,427 and WO-96/00394.
The glazing assembly according to the invention may have a laminated structure, combining in particular at least two rigid substrates of the glass type using at least one sheet of a thermoplastic polymer, so as to have a structure of the glass/stack of thin layers/sheet(s)/glass type. In particular, the polymer may be based on polyvinyl butyral PVB, ethylene-vinyl acetate EVA, polyethylene terephthalate PET or polyvinyl chloride PVC.
The glazing assembly may also have a so-called laminated-glazing structure which combines a rigid substrate of the glass type with at least one sheet of polymer of the polyurethane type having energy absorpton properties optionally combined with another layer of polymers having xe2x80x9cself-healingxe2x80x9d properties. For more details on this type of glazing assembly, reference may be made in particular to Patents EP-0,132,198, EP-0,131,523 and EP-0,389,354. The glazing assembly may then have a structure of the glass/stack of thin layers/sheet(s) of polymer type.
The glazing assemblies according to the invention are capable of undergoing a heat treatment without damaging the stack of thin layers. They are therefore optionally curved and/or toughened. If they are curved, in particular for the purpose of forming windows for vehicles, the stack of thin layers is preferably on an at least partially non-planar face. In a laminated structure, it is preferably in contact with the sheet of polymer.
The glazing assembly may also be curved and/or toughened when it consists only of a single substrate, that provided with the stack. This is then referred to as a xe2x80x9cmonolithicxe2x80x9d glazing assembly. The glazing assembly may also be a multiple-glazing unit, in particular a double-glazing unit, at least the substrate carrying the stack being curved and/or toughened. It is preferable in a multiple-glazing configuration for the stack to be placed so that it is on the side facing the sandwiched gas-filled cavity.
The glazing assemblies of the invention are, in a general way, preferably designed so as to have a light transmission value of from 50 to 85%, in particular from 60 to 80%, with values of reflection RL which are less than 20%, in particular less than 13%, and negative values of a+ and b+ in external reflection: it is thus possible in particular to xe2x80x9ccoverxe2x80x9d the entire range of TL encountered in windows for vehicles, with, in external coloration, a tint more towards the blue-greens, this currently being judged to be quite aesthetic.
The invention also relates to the process for manufacturing the glazing assemblies, which may consist in depositing the stack of thin layers on its class substrate using a vacuum technique of the sputtering type, optionally assisted by a magnetic field (without excluding the possibility that the first layer or first layers is or are deposited using another technique, for example using a thermal decomposition technique of pyrolysis type), and then in carrying out a heat treatment of the bending/toughening or annealing type on the coated substrate without impairing its optical quality.